Eh? Vyse is above Vmca. Why would you be slowing down to Vmca?
Yes, I refine my comment, you're correct. The point I missed making precisely is to not fly significantly faster than the the fastest single engine speed for what you're doing with the plane in low altitude/critical phases of flight, as there will be an increase in asymmetric drag from an unfeathered prop at the faster speed. Yes, increased speed gives more rudder effectiveness, and, more rudder pressure required. I seem to recall getting a pretty tired leg while trimming during some single engine testing in the Turbine DC-3, though the rudder forces lightened with increased rudder deflection! Planes with autofeather are not such a worry in this regard.
Though I do not recall ever testing it, Vyse would be predicated on the prop being feathered. Vmca would be demonstrated before the prop is feathered, though with feathering being an element of maintaining control. If you attempted a Vyse climb without feathering the prop (or couldn't - some Lycomings below a certain RPM) would you have trouble maintaining directional control where flying more slowly would allow you to maintain control more easily? I did some Vmca testing in the Lycoming powered DA-42 during its STC approval, but the details are hazy in my recollection now... The challenge with the Lycoming powered DA-42 is that the power went from 135HP a side to 180HP a side, so there was a lot more asymmetric thrust to overcome. I found by inspection that the less than ideal rudder cable arrangement allowed the rudder pedal to be fully pressed, but the rudder had not reached it's full travel, so "full rudder" was mechanically not available. Vmca was a problem. I did not finish that flight testing, so I don't know what was done to resolve the problem, I just found it...